1. Technical Field
The invention relates to forming cup-shaped members such as container bodies from a blank of metal, and, in particular, to forming such bodies in a double-acting press which reduces the forces exerted on the press by incrementally increasing the pneumatic clamping force exerted on the blank of metal when drawing the container body.
2. Background Information
It is well known in the container-forming art to form two-piece containers, that is, containers in which the walls and bottom of the container are a one-piece member, and the top or end closure is a separate piece, by means of stamping disk-shaped blanks from a strip of metal sheet, and then subsequently drawing the desired configuration into the blank.
In broad terms, the prior art discloses, starting with flat material either in sheet or coil form, blanking material from the sheet stock, and then drawing it into a cup for further redrawing into a final container in the same press or in subsetlent operations. There are a considerable number of prior art patents illustrating various approaches to this formation using either single or double-acting presses. Generally, these prior art presses will simultaneously form a plurality of the container bodies in a single stroke of the single or double-acting press. For example, eight, ten, twelve or more container bodies are formed simultaneously by the single stroke of the press, whether it be a single-action or double-action press.
However, one problem that is encountered with these presses is that they produce excessive noise and forces on the press due to the simultaneous engagement of the initial blank sheet with the plurality of cutting dies or cut edges, followed by the simultaneous pressure holding or clamping engagement of the peripheral edges of the blanks, followed by the simultaneous drawing of all of the cups or container bodies by the movement of a plurality of inner punch or draw members by the inner ram of a double-acting press. These forces present maintenance problems on the dies and press, as well as limiting the number of container bodies or end closure shells which can be produced in a single stroke, or require a larger press having higher tonnages.
The largest forces on the press occur during the pressure-holding or clamping engagement of the peripheral edges of the blanks by the pressure or draw pads. These pressures and forces are considerably larger than those occurring on the press during the blanking of the disks from the sheet metal and the subsequent drawing of the container bodies from the held blanks.
This problem was recognized in U.S. Pat. No. 5,442,947, and in co-pending patent application Ser. No. 08/435,204, which application is assigned to the same assignee as is the present application. This problem appears to be reduced by the method and apparatus of Pat. No. 5,442,947 by providing shims at various locations in the apparatus, so that the clamping pressure is sequentially applied to the peripheries of the blanks to reduce the overall force exerted at the same instant of time on the press during each cycle of the press. This press-loading problem also is reduced by the apparatus and method of the above-identified co-pending application by sequentially blanking all of the disks prior to the sequential clamping of all of the blanked disks against the blank and draw dies, and then followed by the sequential drawing of the container bodies from the clamped disks after the clamping pressure has been sequentially applied to the disks.
However, even though the apparatus and method of the above-described patent and co-pending application helps to reduce the press-loading problem, the apparatus and method of the present invention achieves this result by a completely different operation and modification to existing press constructions.
Thus, it is desirable to produce an apparatus or forming dies and associated method which is capable of producing a single or plurality of container bodies or end shells from steel or aluminum or other stock materials, with a low tonnage press as possible, and with reduced noise and vibrations, while providing the maximum output from the press. However, as indicated above, the forces exerted on the press and dies during the initial blanking, pressure holding and subsequent drawing, limit the output of the press.
Therefore, the need exists for an improved method and apparatus for providing maximum output from a press with as low tonnage rating as possible, while reducing noise and working forces on the press.